1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine etc. and, in particular, to the apparatus capable of improving a productivity particularly in double-sided recording.
2. Related Background Art
An image forming apparatus such a copying machine etc. has been digitized over the recent years, and, with this digitization, a configuration including a discharge portion provided in a spatial area formed within an apparatus main body (which will hereinafter be termed an xe2x80x9cintra-apparatus dischargexe2x80x9d) is widely utilized. At the same time, a sheet fed from a sheet feeding means disposed under the apparatus main body, is conveyed substantially in a perpendicular direction, and an image is recorded on the sheet between it and the discharge portion disposed upward, thereby scheming to decrease a time (for forming the first image) of a first copy by reducing a length of a conveying path. What is practiced in this case is a control method of conveying two or three sheets simultaneously to within the apparatus main body by increasing a conveying speed when reversing and within a double-sided unit and shortening a sheet interval to the greatest possible degree in order to improve the productivity in the double-sided recording.
One of the configurations for the double-sided recording in the conventional image forming apparatuses, is that in the image forming apparatus shown in FIG. 7, the sheet supplied from a sheet supply portion 100 provided under the apparatus is conveyed upwards substantially in the perpendicular direction and is, after an image bearing member 101 has formed an image thereon, discharged to a discharge portion 103 disposed upwardly of the apparatus. A discharge roller 102 serving as a reversing roller reverses a conveying direction of the sheet conveyed to the discharge portion 103 and re-feeds the sheet to the image bearing member 101 through a double-sided conveying path 105 in a double-sided unit 104, thereby forming the images on both of surfaces of the sheet.
According to the configuration for the double-sided recording by the image forming apparatus in the first example of the prior art given above, the conveying roller 102 is used as both of the conveying roller and the reversing roller and is therefore incapable of discharging other sheets during a process of reverting the sheet. Therefore, this apparatus has an advantage of decreasing a production cost, and nevertheless the productivity decreased because of a necessity of widening a sheet interval for reversing the sheet when in the double-sided recording.
Further, in the image forming apparatus in another example of the prior art shown in FIG. 8, the sheet is similarly conveyed upwards substantially in the perpendicular direction from the sheet supply portion 100 provided downwardly of the apparatus and is, after the image bearing member 101 has formed the image thereon, discharged by the discharge roller 102 to the discharge portion 103 provided in the spatial area within the apparatus main body. Herein, a reversing roller 106 provided within a double-sided unit 104 separately from the discharge roller 102, reverses the sheet led to a reverse conveying path 107 within the double-sided unit 104, and thereafter sheet is fed again to the image bearing member 101 via the double-sided conveying path 105 in the double-sided unit 104, thereby forming the images on both of the surfaces of the sheet.
In the configuration in the second example of the prior art, by sharp contrast with the first example of the prior art given above, the productivity in the double-sided recording is improved because of the discharge roller and the reversing roller being different from each other, however, the extra roller and reverse conveying path are needed. Consequently, there arises a problem that the production cost rises and the apparatus increases in its size.
In any case, however, the user was given one option of the configurations for the double-sided recording by the image forming apparatus. Namely, the user must choose any one of the configuration putting more of emphasis on the productivity in the double-sided recording than the cost and the configuration putting the emphasis on the cost in a way that reduces the productivity in the double-sided recording.
Accordingly, it is a primary object of the present invention to provide a sheet conveying apparatus and an image forming apparatus each enabling a user himself or herself to select a plurality of configurations for double-sided recording by use of one common image forming apparatus.
To accomplish the above object, according to one aspect of the present invention, a sheet conveying apparatus has a first reversing member, provided in an apparatus main body, for reversing a sheet on which an image is recorded by an image forming unit, a conveying unit including a second reversing member for reversing the sheet on which the image is recorded by the image forming unit, and so provided as detachably attachable to the apparatus main body, and a double-sided conveying portion for conveying the reversed sheet again to the image forming unit in order to perform double-sided recording.
According to another aspect of the present invention, a sheet conveying apparatus has a discharge roller provided in an apparatus main body and capable of making forward and reverse rotations, this discharge roller discharging a sheet recorded with an image, which is conveyed from an image forming unit, or the discharge roller being capable of reversing the sheet by making its reverse rotations in the middle of discharging the sheet, a double-sided unit including a double-sided conveying path for conveying the sheet reversed by the discharge roller again to the image forming unit, a conveying unit including a reversing roller, so provided as to make forward and reverse rotations, for reversing the sheet by its making reverse rotations in the middle of conveying the sheet recorded with the image, which is sent from the image forming unit, and a unit conveying path for conveying the sheet reversed by the reversing roller, this conveying unit being so provided as to be detachably attachable to the apparatus main body, wherein when the conveying unit is attached to the apparatus main body, the unit conveying path is connected to the double-sided conveying path.